Question

The correct option(s) regarding the complex $\left[Co\right(en\left)\right(N{H}_3{)}_3\left(H_{2}O\right){]}^{3+}$ $(en=H_{2}NC{H}_{2}C{H}_{2}N{H}_2)$ is/are:

• A. It has two geometrical isomers.
• B. It will have three geometrical isomers if bidentate 'en' is replaced by two cyanide ligands.
• C. It is paramagnetic.
• D. It absorbs light at a longer wavelength as compared to $\left[Co\right(en\left)\right(N{H}_3{)}_4{]}^{3+}$.

Answer 1

Answer: (A), (B), (D)

It will have three geometrical isomers if bidentate 'en' is replaced by two cyanide ligands.
It has two geometrical isomers.
It absorbs light at a longer wavelength as compared to $\left[Co\right(en\left)\right(N{H}_3{)}_4{]}^{3+}$.

(A) $\left[Co\right(en\left)\right(N{H}_3{)}_3\left(H_{2}O\right){]}^{+3}$ complex is type of $\left[M\right(AA\left)b_{3}c\right]$ which will have two geometrical isomers.

(B) If $\left(en\right)$ is replaced by two cyanide ligand, complex will be type of $\left[M{a}_3{b}_{2}c\right]$ and have 3 geometrical isomers.

(C) $\left[Co\right(en\left)\right(N{H}_3{)}_3\left(H_{2}O\right){]}^{3+}$ have $d^6$ configuration $\left(t_{2g}^6\right)$ on central metal with strong field ligands, therefore it is diamagnetic in nature.

(D) Complex $\left[Co\right(en\left)\right(N{H}_3{)}_3\left(H_{2}O\right){]}^{3+}$ have lesser $CFSE\left({△}_0\right)$ value than $\left[Co\right(en\left)\right(N{H}_3{)}_4{]}^{3+}$ therefore complex $\left[Co\right(en\left)\right(N{H}_3{)}_3\left(H_{2}O\right){]}^{+}$ absorbs longer wavelength for $d-d$ transition.